1. Technical Field
The present invention relates to an improved spindle hub assembly for mounting storage disks for rotation within in a hard disk drive, and more particularly relates to an improved spindle hub assembly in which a dummy disk is used as a buffer between a disk clamp and storage disks to absorb spurious vibrations and minimize stress concentrations and disk distortion when the storage disks are mounted for rotation within the hard disk drive.
2. Background Art
Generally, disk drives can be grouped into magnetic disk drives such as a floppy disk drive and a hard disk drive which are used as an auxiliary memory in a computer, and optical disk drives such as a compact disk-read only memory (CD-ROM) and a magneto optical disk drive which are used as media in a multimedia environment including audio, video and alike.
In a hard disk drive used as an auxiliary memory for a computer, a magnetic head floating on a recording surface of the magnetic disk at a predetermined flying height operates for recording and reproducing data on the magnetic disk through magnetic flux. Accordingly, in order to increase data storage capacity of the magnetic disk drive and other data storage devices, it is of importance that a recording density of the magnetic information on the magnetic disk is enhanced, and that the magnetic disk drive is packaged with as many disk as possible.
As the recording density of magnetic disks is enhanced however, the flying height of the magnetic head becomes inversely minimal. A standard minimum flying height of the magnetic head is approximately 0.2 .mu.m or so. Thus, the stability of the head flying height must be accurately maintained in order to realize a large capacity construction and high reliability of the magnetic disk drive. This requires a high degree of flatness of a rotating magnetic disk which can be ascribed to the way in which the disk is mounted to a hard disk spindle assembly. Such spindle assembly as disclosed, for example, in U.S. Pat. No. 5,295,029 for Disk Drive Including Unitary Deck For Aligning And Supporting Axially Retractable Spindle Assembly issued to Elsing et al., U.S. Pat. No. 5,189,577 for A Magnetic Disk Apparatus And A Motor Securement Therefor issued to Nishida et al., U.S. Pat. No. 5,136,450 for Disk Pack Assembly Having A Laminate Sleeve Disposed Between A Spindle And A Disc For Reducing Radial Disc Displacement issued to Moir, and U.S. Pat. No. 5,031,061 for Disk Drive Hub Assembly issued to Hatch, typically includes a rotatable spindle hub that is carded by a fixed spindle shaft securely mounted to the housing. A plurality of information storage disks are journaled about the spindle hub. Spacer disks are provided between adjacent information storage disks. The vertically aligned information storage disks are clamped to the spindle hub by a disk clamp secured by a plurality of screws.
In practice, the disk clamp design in relation with the hard disk spindle assembly is critical to high performance disk drives and there are several design criteria that must be met in order to provide an effective disk clamp. Specifically, the disk clamp must provide a uniform clamping force along its clamping surface to avoid problems such as top disk distortion. The disk damp must also be designed to uniformly distribute its internal stress in order to minimize clamping force variations due to thermal expansions. Many conventional disk clamp designs in which screws are used to secure the disk clamp to the spindle hub such as those disclosed in Elsing et al. '029, Nishida et al. '450, Moir '450, and Hatch '061, tend to loosen after time and stress imbalances within the clamp. Other convention disk clamp designs are disclosed, for example, in U.S. Pat. No. 5,305,163 for Stationary Angularly Aligned Stationary Spindle Shaft issued to Holm, U.S. Pat. No. 5,155,640 for Disk Spindle Motor Cap issued to Lee, U.S. Pat. No. 5,101,306 for Releasable Controlled Force Clamp For Disk Storage Apparatus issued to Johnson, U.S. Pat. No. 5,056,082 for Apparatus For Clamping Removable Disks and U.S. Pat. No. 5,048,005 for Spindle Clamp Having A Unitary Lock Member issued to Ekhoff also suffer similar drawbacks.
More recent disk clamp designs as disclosed, for example, in U.S. Pat. No. 5,490,024 for Disk Clamp Having An Annular Section Of Increased Rigidity issued to Briggs et al., U.S. Pat. No. 5,392,178 for Motor For A Disc Driving Device Having A Hub Positioned On Inner Race Of An Upper Bearing issued to Nishio et al., and U.S. Pat. No. 5,274,517 for Disk Clamp With Annular Spring Section issued to Chen are better served to provide a uniform clamping force and minimize stress concentrations within the disk clamp. For example, Chen '517 discloses a disk clamp that includes a substantially flat inner ring, an outer ring having a rounded engaging surface and a circular convex spring section that couples the inner ring section to the outer ring section. When installed on the top portion of the spindle hub by a plurality of screws through corresponding screw holes of the inner ring section, the disk clamp will contact at the rounded engaging surface of the dome-shaped resilient spring section in order to minimize adverse consequences to the disks. Similarly, Nishio et al. '178 also discloses a disk clamp that acts as a plate spring for securing the plurality of information storage disks to the spindle hub. In Nishio et al. '178 however, the disk clamp is secured to the spindle hub way a single screw, rather than a plurality of screws, mounted to a center bore of the spindle hub. In Briggs et al. '024, a disk clamp includes a raised circular wall around an outer radius of the clamp serving to increase the structural rigidity of the clamp in a single axial section of the claim in order to provide a stress barrier to the transmission of localized stresses from the screw points. Such conventional disk clamp designs for a spindle hub assembly, as I have observed however, continue to distort a clamping surface and cause deformity of the clamped storage disk over a time period when pressure asserted onto the storage disk by the disk clamp is uneven or too extreme. The disk distortion, of course, affects the flatness of the storage disk and alters the flying height of the magnetic head which ultimately attribute to the generation of operational errors during recording and reproduction of data.